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How to hash a number, and check the result in a solidity contract (probably data type confusion)
edmundedgar
Member Posts: 19 ✭✭
in Solidity
I'm trying to make a hash of a number (in python) then have a solidity contract recreate the hash, then do something useful with the number.
(The motivation for this is that I ultimately want to sign the data and pass in the signature, then check it using ecrecover to validate the data, which is all working fine apart from the hashing part.)
https://github.com/edmundedgar/show-confusion-about-solidity-types-and-sha3/blob/master/test.py
It's working fine for me if I hash a string, and pass the string into the contract. But then I'm stuck with a string in my contract, and I don't know how to change that into an int or do anything useful with it.
https://github.com/edmundedgar/show-confusion-about-solidity-types-and-sha3/blob/master/hash_checker_string.sol
If I pass the contract bytes32 or int256 and call sha3() on that it produces some kind of hash, but I can't work out exactly what it's hashing, or how I would create the same hash myself in Python.
Can anyone tell me how to do any of:
a) Recreate the hash I'm getting in the contract outside the contract
b) Pass in the data to the contract in such a way that it creates the hash I'm making outside the contract
c) Change the string that I'm successfully hashing right now into bytes32 or int256 inside the contract?
(The motivation for this is that I ultimately want to sign the data and pass in the signature, then check it using ecrecover to validate the data, which is all working fine apart from the hashing part.)
https://github.com/edmundedgar/show-confusion-about-solidity-types-and-sha3/blob/master/test.py
It's working fine for me if I hash a string, and pass the string into the contract. But then I'm stuck with a string in my contract, and I don't know how to change that into an int or do anything useful with it.
https://github.com/edmundedgar/show-confusion-about-solidity-types-and-sha3/blob/master/hash_checker_string.sol
If I pass the contract bytes32 or int256 and call sha3() on that it produces some kind of hash, but I can't work out exactly what it's hashing, or how I would create the same hash myself in Python.
Can anyone tell me how to do any of:
a) Recreate the hash I'm getting in the contract outside the contract
b) Pass in the data to the contract in such a way that it creates the hash I'm making outside the contract
c) Change the string that I'm successfully hashing right now into bytes32 or int256 inside the contract?
Comments
In case anyone else is wondering, you make the hash outside the contract like this to match what the contract is doing:
sha3_256(decode_hex(format(mynum, 'x').zfill(64))).digest()ie
* Start with a number
* Hex-encode-it
* Pad the left side with zeros to make up to 64 hex characters (as it's going to go into 32 bytes)
* Decode the hex again, and you're ready to hash.
Solidity's sha3 is applied to its arguments without padding. This means that sha3(uint8(2)) should be equal to
sha3_256(decode_hex('02')).digest()
and
string s = "abc";
sha3(s);
produces
sha3_256("abc").digest()